Dxers Unlimited

Dxers Unlimited's weekend edition for 7-8 February 2004

By Arnie Coro

radio amateur CO2KK




Hi amigos radioaficionados around the world and in space!

Welcome to the weekend edition of your favorite radio hobby program, coming to you from Havana, now
also on new short wave frequency from 05 to 07 UTC on 9655 kiloHertz, with our East Coast of North
America rhombic antenna. Reports of this new Radio Havana Cuba frequency can be sent directly to
me:via e-mail to arnie@rhc.cu, again, arnie @rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana
Cuba, Havana Cuba.. A nice new QSL card will be sent to all listeners reporting our new 9655
frequency. Item two: Also related to our new transmitters now testing ... 11760 kiloHertz, Radio
Havana Cuba's classic frequency from the very early days we went on the air with the now retired
Brown Boveri Swiss made transmitters, is also on the air from 05 to 07 hours UTC in English, and
using an antenna designed by my mentor, Dr. Jose A Valladares Ph.D, one of Cuba's most prestigious
and well known professional radio engineers. Pepe Valladares, as we affectionaly call him, designed,
way back in 1961 a beautiful wide band dipole antenna, that works from 9 to 18 megaHertz with a very
low standing wave ratio. Pepe's dipole, as we have known that antenna for now a bit more than 40
years is proudly standing at the entrance of our Bauta transmitter site, and is now fed by a new
transmitter. The wide band dipole is oriented with its main axis 160 degrees to 340 degrees azimuth,
providing an excellent coverage of North, Central and South America as well as part of the
Caribbean... Again, 11760 kHz is on the air with our English language programs between 05 and 07
hours UTC, and also during our early afternoon local Havana time broadcast to the Caribbean and the
Southern United States at 21 hours UTC . Item three: Micro Vert antenna experiments continue, and my
good friends Jose Angel Amador, CO2JA and George Murphy VE3ERP continue to polish the GW BASIC
software designed to calculate the antenna. George has now added more information that will guide
you on how to build this very interesting and rather unusual antenna system. By the way, I just
built one from scratch in less than an hour. It was cut for the 10 meters band, and it seems to be
working quite well.. You can send for the latest version of the MICRO VERT antenna software
available as freeware, just send an e-mail to arnie@rhc.cu, and you will receive the extremely small
sized software written using the classic legacy GW BASIC programming language... Item four today
will be devoted to our technical topics section mixed with ASK Arnie.... and as always at the end of
the show, our exclusive and not copyrighted HF propagation update and forecast will complete today's
Dxers Unlimited's weekend edition coming to your Havana, I am Arnie Coro, radio amateur CO2KK back
with you all in just a few seconds...




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Si amigos you are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and here
is our antenna topics section... once again dealing today with the ultra compact single band MICRO
VERT capacitive probe antenna system. As I said just a minute ago, I stumbled across a roll of RG58
U coaxial cable on Thurday... and decided that it had enough length to try to build a MICRO VERT for
the 10 meters band...The reason for choosing 10 meters is that I happen to own a little nice 10
meters band 25 Watt transceiver, that was just waiting for a dedicated antenna system for monitoring
the band. As many radio amateurs know, and unfortunately also many radio amateurs also don't know,
10 meters is a very surprising band, and it is open for Dxing much more time that what anyone can
imagine. If you happen to own one of those Rat Shack HTX 100 or HTX 10 single band 10 meters
transceivers, don't push them aside until the next solar maximum... Just build a single band antenna
for them and monitor the beacons segment from 28.2 to 28.3 megaHertz, and amigos, you will be
pleasently surprised to watch how often 10 meters is open for Dx !!! Well,back to my MICRO VERT for
10, that was built in just a little more than one hour... The capacitive probe radiator for 10
meters is amazingly small... so don't be surprised, when you run the software to calculate the
antenna and it comes out with a capacitive probe length of just 6.5 inches or 21.3 centimeters of
the one inch or 25 millimeters diameter aluminum tube that is the actual radiator of this antenna
system... The coil was wound using number 18 enamelled wire using also a one inch or 25 millimeters,
diameter PVC plastic pipe as a coil form...For those already having the program installed on their
computers, the center design frequency of 28.5 gave the following results... probe length 165
millimeters or 6.5 inches, the capacity of the probe 11.33 picofarads, the required inductance 2.75
microHenries and the coaxial cable counterpoise length 2.04 meters, the RF choke coil was wound
using a 50 millimeters or two inch diameter PVC plastic pipe as the coil form, and I wound 8 turns
kept tightly wrapped to the pipe using plastic cable ties. AH. Before I forget... the coil wound
with number 18 enamelled wire has 15 turns closewound , kept together by wrapping PVC high quality
electricians tape...

I installed the antenna on my terrace rail for a test, and was pleasently surprised to pick up
several beacons at around four PM local time, that's 21 hours UTC... In order to test the antenna by
comparison, I also built a 10 meters band full size dipole,and installed at the same
height...feeding both antennas to a switch...After several tests, both receiving and transmitting, I
arrive to a preliminary conclusion... The MICRO VERT is an amazing antenna, considering its
extremely small size and low profile...The typical difference between the two antennas during last
Thursday afternoon tests was between minus 6 and minus 10 to 12 decibels...as expected by the
results of two popular antenna modeling programs... So amigos, if you are really short of antenna
installation space, maybe a single band MICRO VERT will let you operate on the HF bands...Remember
that this is an easy to homebrew antenna, made with very low cost materials, so you have nothing to
loose by building one and testing it under your particular operating conditions... The MICRO VERT
antenna information package is free for the asking, just send your request to arnie@rhc.cu, again
arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro,Radio Havana Cuba, Havana, Cuba....

......

>From Havana, via shortwave and streaming audio from www.radiohc.cu this is Dxers Unlimited's weekend
edition amigos...Now a combination of technical topics plus Ask Arnie... Hope you enjoy it...
Several listeners building their own receivers have asked about the use of old vacuum tubes and how
they can really know if they are good or not... Well my friends, the easiest tube test that you can
do... is replacing one vacuum tube with another one that is brand new , out of the box and tested
using a professional vacuum tube transconductance tester... But professional vacuum tube testers are
becoming as rare as the extinct proverbial DODO bird !!! So, the best thing you can do is to build
yourself a homebrew vacuum tube tester,something I did a number of years ago very succesfully. The
circuit used is capable of testing many different types of tubes, and it provides very consistent
results...For those of you involved in vintage radio technology, the vacuum tube tester is an almost
essential tool... !!!

And now amigos, just before going QRT, here is our exclusive and not copyrighted HF propagation
update and forecast... solar flux is hovering around 100 to 110 units and holding steady with solar
activity described at this moment as LOW... Expect more coronal holes generating high speed solar
wind bursts during the next several days. The peak sunspot count for this solar rotation will
probably be going not higher than about 120 and that count won't hold for a long time as the solar
cycle continues its downward slope. Nevertheless, solar flux is still high enough to support peak
maximum useable frequencies as high as 28 or 29 megaHertz during short periods that amateur radio
operators can put to very good use working DX on the 15, 12 and 10 meter bands while it lasts !!!See
you all at the mid week edition of Dxers Unlimited, and don't forget to take a little time to send
me your comments about the program and any radio hobby related question you will like me to try to
answer... send mail to arnie@rhc.cu and VIA AIR MAIL, a postcard will be fine to Arnie Coro, Radio
Havana Cuba, Havana Cuba